TISSUES
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TISSUES A COLLECTION OF CELLS THAT PERFORM A SPECIFIC FUNCTION Meristems Unlike animals, plants have permanent regions of cell division Meristems Growth Meristems Apical Meristems Cell division at tips of roots and stems Produce primary tissue Meristems Lateral Meristems Cell division that increases girth of roots and stems Secondary growth Lateral Meristems Vascular cambium Conduction “Plumbing” Lateral Meristems Vascular cambium Cambium Thin cylinder of brick-shaped cells Majority of growth contributes to increased girth Lateral Meristems Cork cambium Layer of cells outside vascular cambium Inside the outer bark Lateral Meristems Intercalary Meristems Grassy plants Develop nodes along stems Lateral Meristems Intercalary Meristems Do not contain cork cambium Vascular bundles Tissues Simple Tissues Parenchyma Collenchyma Sclerenchyma Simple Tissue Parenchyma cells Thin, pliable cell walls The most abundant of all cell types Space between parenchyma cells Intercellular space Simple Tissue Parenchyma cells that contain numerous chloroplasts Chlorenchyma tissue Primarily photosynthesis Parenchyma cells lacking chlorophyll Food and water storage Soft, edible parts of fruit and vegetables Simple Tissue Collenchyma cells thicker and longer Primarily just below the epidermis Flexible support for growing tissue Strands of celery Simple Tissue Sclerenchyma cells thickest and toughest cell walls Impregnated with lignin for support Simple Tissue Sclerenchyma cells form two types of tissues Form very hard tissue Sclereids Gritty texture of pear Hard shell of nuts Simple Tissue Sclerenchyma cells form two types of tissues Longer tissue that contain a tiny cavity (lumen) Fibers Complex Tissue Composed of two or more types of cells Complex tissue Complex Tissue Plumbing tissues Xylem Phloem DICOT MONOCOT Complex Tissue Xylem Conducts water and minerals from the roots Transports upward Complex Tissue Xylem Long tubes composed of vessel elements Vessels Large openings at each end allow for water flow Complex Tissue Xylem Vessel elements that are dead at maturity Tracheid Thick secondary cell walls Center of tree trunk Complex Tissue Xylem Openings along cell walls connect side by side cells Pits Lateral flow in trees Rays Complex Tissue Phloem Conduct dissolved food (sugars) from photosynthesis Conductive tissue composed of sieve tubes Transports downward Similar to xylem vessels Perforated ends instead of large openings Sieve plates Complex Tissue Phloem Conductive tissue composed of sieve tubes Similar to xylem vessels Complex Tissue Phloem Perforated ends instead of large openings Sieve plates Complex Tissue Phloem Living sieve tube cells contain callose Injury will result in callose to plug sieve plate Callus plug Plants seal, not heal Xylem and Phloem https://www.youtube.com/watch?v=LQ03xIkLLQU Complex Tissue Epidermis Outermost layer of cells Skin Complex Tissue Epidermis One cell thick (usually) Multilayered examples Orchid aerial roots Velamen roots Complex Tissue Epidermis Secrete fatty (waxy) substance Cutin Protective layer on the outside Cuticle Restricts water loss Resists disease and insects Complex Tissue Epidermis Form tubular extensions Root and foliar hairs Complex Tissue Epidermis Openings along surface Stomata Gas exchange Transpiration Complex Tissue Epidermis Guard cells Open and close Complex Tissue In woody plants, epidermis sloughed off Periderm Outer bark Boxy cork cells Complex Tissue Contain fatty substance to waterproof layer Suberin Protects phloem tissue beneath it Complex Tissue Pockets of tissue protruding through periderm Lenticels Gas exchange Fig. 4.14 Complex Tissue Secretory cells Exude nectar, fragrance or oil Expel waste from cells
